Reforming Carbon Accounting for Modern Power Systems

Florian Berg, Christopher R. Knittel, and Jack Morris

November 2026

The Greenhouse Gas Protocol and the Science Based Targets initiative, which together govern the climate claims of most large companies, are both revising their rules for emissions from purchased electricity. The proposed changes, including hourly matching, deliverability requirements, and commissioning-date limits for energy attribute certificates, would make emissions inventories more accurate. On today’s congested, transmission-constrained grids, however, they still cannot show whether a corporate action actually reduced grid emissions. We argue that both standard-setters should keep attributional inventories but also require a consequential assessment, based on locational marginal emissions (LMEs), for any claim of progress toward net-zero targets, and should recognize certificates for storage and transmission investments. Applying three accounting methods to 2023 PJM data around the Loudoun County, Virginia data-center cluster, we find that the emissions induced by a new 10-MW data center are 73–81% higher under LMEs than under annual grid averages, while hourly matching barely changes measured impacts relative to current practice. Consequential accounting also reverses the ranking of solar sites, shows battery storage reducing emissions rather than adding to them, and is the only one of the three methods that gives transmission upgrades any credit.